Wednesday, April 17, 2013

A recent study from University of Toronto PhD student Sacha Kapoor and Arvind Magesan evaluated the impact of installing pedestrian countdown timers at various intersections throughout Toronto over a four-year period. After much parsing of data, the study concluded that installing countdown signals resulted in a five-percent increase in crashes versus intersections without the special signals. But there are nuances to that conclusion:

"The data reveals starkly diﬀerent eﬀects for collisions involving pedestrians and those involving automobiles only. Although they reduce the number of pedestrians struck by automobiles, countdowns increased the number of collisions between automobiles. We show that countdowns cause fewer minor injuries among pedestrians for every pedestrian on the road and more rear ends among cars for every car on the road."

Further, while the the countdown signals increase crashes overall, at the most dangerous intersections the installation of countdown signals reduced crashesand made the intersections safer.

Unfortunately, nuances don't fit nicely into a soundbite. If you scroll through headlines of recent stories covering this study, you'll see two themes emerge:

Pedestrian countdown timers cause more crashes

Pedestrian countdown timers safer for pedestrians, hurt drivers

Neither of these statements is false, but they also don't tell the whole story about the effects of the signals. More importantly, if you're a policymaker faced with a decision about whether or not to install countdown signals, they could easily lead you to the wrong conclusion.

It would be easy for a politician in a cash-strapped city (and what city isn't, these days?) to glance at the headlines and decide that countdown signals weren't worth the price. Or for a frustrated driver to wave this study around as evidence that a countdown signal should be removed. (You hear the same kind of arguments all the time in discussions of marked crosswalks --many people still think they give pedestrians a "false sense of security" based on a superficial reading of one antiquated study, and insist they be removed.) But if you read the actual conclusions of the study, you'll find two key recommendations:

Modify countdown signals to hide them from drivers. The signals provide significant improvements to pedestrian safety, so eliminating them entirely would mean giving up those benefits--even if it would also reduce rear-end crashes. Instead, the study authors recommend a compromise:

"The ﬁndings imply authorities can improve welfare by sharing the information with pedestrians and hiding it from drivers. For example, rather than making countdowns visible, the traﬃc authority might announce the time until a light change through a speaker that only pedestrians can hear."

Install countdown signals only at dangerous intersections. While it might not be good policy to install countdown signals at every signal in a city, that doesn't mean they shouldn't be installed everywhere. Because the countdown signals improve safety at the especially dangerous intersections, the authors suggest that:

"...cities might beneﬁt from installing countdowns at dangerous intersections and not at safe ones."

It's easy to jump to conclusions about studies based on headlines, but decisions about infrastructure should be based on a more thorough evaluation of the evidence--particularly when pedestrian safety is at stake.